Papers by Keyword: Catalyst Layer

Abstract: Physical parameters effects are considered as sticking point to increase and decrease the electrode performance for PEMFCs, which is related to the electrode structural degradation under diverse operating conditions, such as various air and hydrogen pressures, humidifier temperatures, and air and hydrogen flow rates. The operating for electrode prepared with 20 wt% Pt loaded 0.3 mg_Pt/cm² in single cell (25 cm²) showed that diverse parameters as pressures, humidifier temperatures, flow rate of air /hydrogen have an effects on the electrode performance. Results show better power density for high pressure, high air flow rate, and for low humidifier temperature, low H₂ flow rate. The increase in pressure ratio results increases in the current density and power density from 91.96 to 99.96 mA/cm² and from 32.56{mW/cm²} to 35.48 {mW/cm²} for an air/H₂ ratio of 1/0.5 bar and 3/2 bar, respectively. The hydrogen and air flow with the stoichiometry coefficient ratio 2/1 is the best value to achieve better performance by a flow rate of 0.3 L/min for H₂ and 0.6 L/min for air, which correspond to a current density and power density of 103.96{mA/cm²} and 31.56{mW/cm²}.

Abstract: A two-dimensional steady state numerical model for high temperature polymer exchange membrane fuel cells based on Nafion212/SiO₂ composite membrane was developed. Finite element method was used to solve electrochemical kinetics coupled with flow, multi-component transport, charge balance and energy conservation. The model-predicted fuel cell polarization curve was compared with the published experimental result and a good agreement was found. The effects of the structure parameters of the catalyst layer including Pt/Carbon ratio and Pt loading on the performance of high temperature polymer exchange membrane fuel cells were evaluated.

Abstract: The electrodes in Unitized Reversible Fuel Cell system with supported platinum carbon black are reported. However, the electrodes in the system is consist two internal modes; it is electrolyzer and fuel cell mode. A Unitized Reversible Fuel Cell has dual function electrodes are joined in the same cell to reduce the volume and improvement efficiency performance. The electrodes of Unitized Reversible Fuel Cells operating on hydrogen and oxygen which have as high as efficiency at most the applications. Therefore, This article is concentrated on the preparation of bifunctional electrodes as design and material with low platinum loading and supported by platinum carbon black and characterization by using scanning electron microscopy. As well as, survey the latest literature on bifunctional electrodes and electrocatalysts to identify the major problems occur in design of the URFC electrodes.

Abstract: This paper summarizes the performance of PEMFC catalyst layer. The main materials used as catalyst in PEMFC are presented as well as the typical structure of MEA. Functions of catalyst during the operation of PEMFC are discussed in detail. Catalyst plays a key role in accelerating the rate of electrochemical reaction, especially that of reduction with oxygen in cathode. But its high cost and low tolerance for has resulted in a severe fact that essentially all the longevity of PEMFC which adopts precious metal-platinum or platinum alloys as catalysts is relatively short. A sputter deposited method is presented to enhance the efficiency of catalyst in PEMFC, while whether this method would bring about a striking effect or not remains worth further researches.

Abstract: A mathematical model for the simulation of the transport phenomena occurred in the anode of a typical fuel cell is presented here. The model initially considers a simple onedimensional geometry where the mass transport equation is combined with a Tafel-type description for the current density. By assuming isothermal conditions, the numerical solution of the differential equations was achieved with the use of a non-linear shooting scheme in conjunction with the multidimensional Newton algorithm. The space was discretized through a constant-step mesh while the resulting nonlinear system of ordinary differential equations was solved by using the 4th order Runge-Kutta method. The whole algorithm was implemented by developing a new FORTRAN code. In addition, a planar two-dimensional geometry is also considered, where the mass transport is described by the convection-diffusion equation within the catalyst layer together with the Navier- Stokes equation for laminar flow conditions and the electrochemical effects, while the convective heat transfer within the developed diffusion layer is also taken into account. This approach has been numerically implemented and solved by using the finite volume method being applicable through the CFD-RC© commercial package. For the sake of simplicity, the feedstream of the fuel cell was assumed to be a hydrogen-rich mixture (H2 >90%) for all cases. Both SOFC and PEM type fuel cells were considered in this study, while the results are presented in terms of fuel concentration, produced current density and overpotential.

Abstract: A mathematical model for an ultra-thin catalyst layer in PEFCs is introduced. It utilizes Nernst-Planck and Poisson equations. Calculated polarization curves are shown to compare favourably with published experimental data for ultra-thin catalyst layers. Aspects of current conversion, reactant, current distribution, and catalyst utilization are explored. The effect of catalyst layers thickness on the Pt utilization is discussed. This study gives us a better understanding of transport and reaction at the mesoscopic scale and it furnishes the directions for optimization of this type of catalyst layer.